You may not know it, but you’ve probably seen Alistair Tidey’s house already, either on the front of a glossy calendar, or spread across several pages in a “homes to die for” magazine.

The fact is, whenever publishers want to illustrate the joys of rural Italy, they reach for a shot of Podere Belvedere, Tidey’s six-bedroom mansion in southern Tuscany. Perched on a tree-ringed hillock, the property is surrounded not just by olive groves, but by hills that undulate as far as the eye can see.

“From my house, you can count the number of buildings visible, and it comes to barely 20,” says Tidey, an Irish property developer who bought his Italian idyll eight years ago for €2.7 million (£1.9m) . He spent more than €1 million renovating it and is now selling it for €6m (£5.4m) .

“The best thing about the view is that it’s changing all the time,” he says. “Not only does the landscape go from gold to green to brown at different times of the year, but the colours are constantly shifting throughout the course of a single day.”

What’s more, there’s no prospect of that view being spoilt. The surrounding Val d’Orcia area has been declared a Unesco World Heritage site. This means there’s as much chance of apartment blocks going up as there is of a high-rise being built on the Acropolis.

“The kind of people who are going to be interested in this property are those who are making a lifestyle purchase, rather than a forced buy,” says Claire Hazle of Knight Frank’s international division. “It’s not so much a must-have transaction, as an I-want. And what they want is a place where both the view and the value are protected.”

Don’t we all? The trouble is, there aren’t many places where you can guarantee the landscape won’t get blotted. Unless, of course, you’re looking out to sea, as you are at lovely Castle Gayer, at Marazion, in Cornwall (on the market for £2.75m).

Not only does this seven-bedroom Victorian residence have its own beach (owned by the National Trust), it also looks out both on to the open ocean and on to St Michael’s Mount, the English version of Mont St Michel. This fulfils the three perfect-view requirements of Edward Heaton, experienced housefinder for homesearch agents Property Vision.

“First of all, you should be able to see for a distance of at least two miles, but preferably between 10 and 20,” he says. “Next, you want as all-round a view as you can get, definitely 180 degrees, and ideally 360. Finally, the view should be as natural as possible, with a minimum number of man-made structures. These days, that includes wind turbines. Before recommending a property, we commission a specialist firm to investigate the likelihood or otherwise of a wind farm being built at some point in the future.”

As to how much a turbine-free view adds to the value of a home, though, agents are reluctant to name a figure.

“About 30 to 40 per cent of our buyers say they will pay more for a nice view, but only five per cent say it is absolutely essential,” says

James Grillo, of the country house department at Chesterton Humberts.

“We recently sold a spectacular 56-acre property, with views across to Chichester Cathedral, and a 1,000ft frontage on to Chichester Harbour. Had that same property been tucked away in the South Downs, I reckon it would have cost 30 per cent less.”

Mind you, such dramatic differences of view (and therefore price) are rarer in the countryside, than in town. Especially when there’s water involved.

“At the Riverside Quarter in Wandsworth, you’ll pay £900 per square foot for a two-bedroom apartment with a river view, as against £700-£800 for the same-sized apartment without a river view,” says Robin Chatwin, director of residential sales at Savills estate agents.

“That said, there aren’t that many smaller apartments, at least in the centre of town, which have a river view. In most developments, the apartments with the nice views are the biggest and most expensive.”

Speaking of which, Edward Heaton has a theory that prices are more affected by ugly views than pretty ones. “I’d say a good view adds only 10 per cent to the value,” he says. “But a bad view can reduce it by as much as 25 per cent.”

And in the final analysis, Grillo believes that the house itself is more important than the view. “We’re all a bit vain, so we like to show off our homes and hear admiring comments,” he says. “It’s more important what people see when they look at our house, rather than what we see when we look out of it.”

For sale

Tom-An-Oir is a lochside hideaway on the peaceful shores of Loch Garry, with breathtaking views and four acres of unspoilt grounds. It includes four double bedrooms, a games room, a luxurious sitting-room and a spacious double garage. Available from Knight Frank for £475,000 (0131 222 9600; www.knightfrank.co.uk).

Oversea House is a secluded coastal paradise near Blackpool Sands in Devon. It has four double bedrooms, separate guest accommodation and an outdoor pool. A spectacular main sitting-room with full-width windows overlooks the sea. Available from Knight Frank at £1.5m (01392 423111; www.knightfrank.co.uk).

This fifth-floor apartment in the Cimiez Regina boasts a stunning 180-degree view across Nice and the French Riviera. With elegant cornices, wrought iron fittings and marble floors, the house also has a pool, tennis court, and two-car garage. From Savills for £737,500 (020 7016 3740; www.savills.com/international).

Podere Belvedere is on the market for £5.4 million with Knight Frank (020 7629 8171; www.knightfrank.com)